Personally I would never use epoxy as a sealer over body work and filler. As I mentioed epoxies are very sensitive to the type of material they are being sprayed over. Epoxies are also designed and developed to be sprayed directly on metal not over filler.

Please provide links to back up these questionable assertions, because I have never seen any epoxy tech sheet that restricts allowable substrates in such a way. The only restrictions I have seen have to do with TPA (lacquer), type of metal conditioning, and acid-etch primers, and of course the normal requirement for adhesion promoter over certain types of TPO, etc.

All epoxies I have dealt with are IDEAL primers for application over plastic filler.